Season-long exposure of bilberry plants to realistic and future ozone pollution improves the nutraceutical quality of fruits

Ozone (O-3) is a phytotoxic air pollutant capable of limiting plant yield and growth, and altering the quality of edible plant products. This study aimed to investigate the effects of long-term O-3 exposure at realistic and future concentrations (applied during fruit development) not only on morphological, physiological, and biochemical plant/leaf traits of Vaccinium myrtillus but also on its fruit yield and quality. Three-year-old saplings were grown from May to July under three levels of O-3 concentration [1.0, 1.5 and 2.0 times the ambient air concentrations, denoted as AA, 1.5_AA and 2.0_AA], using a new-generation O-3 Free Air Controlled Exposure system. Ozone induced oxidative prmum and membrane denaturation as confirmed by the accumulation of anion superoxide, hydrogen peroxide (center dot O-2(-): +39 and + 29%; H2O2: + 55 and + 59% in 1.5_AA and 2.0_AA, respectively, compared with AA), and malondialdehyde by-product (1.4- and 2.5-fold higher than AA, in 1.5_AA and 2.0_AA, respectively). The observed oxidative burst likely affected several cellular structures interested by photosynthetic processes (e.g., decrease of the maximum rate of carboxylation: -30%). This constraint likely induced a decline in plant vitality and a different partitioning of biomass allocation between above and below organs. An accelerated maturation of bilberries due to O-3 was reported, suggesting that plants grown under harsher environmental conditions suffered from metabolic changes associated with early ripening. Increasing O-3 concentrations might be responsible for an alteration of the ratio between oxidation and reduction processes mechanisms that was followed by a loss of integrity of membranes, so limiting the availability of energy/resources, triggering enzymatic oxidation of phenols to red/purple pigments, and promoting fruit maturation. To the best of our knowledge, this is the first research showing that long-term O-3 exposure during bilberry fruit development influenced not only several plant/leaf traits, but also fruit nutraccutical quality at the time of harvest.